A wide variety of catalyst systems can be used in the polymerization of diene monomers, such as 1,3-butadiene or isoprene, into polymers. For instance, anionic polymerization techniques that utilize alkyl lithium initiators can be used to polymerize 1,3-butadiene into polybutadiene rubber or to polymerize isoprene into polyisoprene rubber. Copolymers of diene monomers and vinyl aromatic monomers, such as styrene, can also be made by anionic polymerization techniques. For instance, anionic polymerization techniques can be used to copolymerize 1,3-butadiene and styrene to make styrene-butadiene rubber (SBR).
U.S. Pat. No. 5,906,956 discloses an initiator system which is comprised of (a) a lithium initiator, (b) a sodium alkoxide, and (c) a polar modifier. This anionic system can be used to polymerize 1,3-butadiene into polybutadiene having a high vinyl content or to polymerize isoprene into polyisoprene having a high 3,4-isomer content.
U.S. Pat. No. 5,753,579 discloses a process for synthesizing polymers having high trans-isomer contents with an initiator system which is comprised of (a) at least one organolithium or organomagnesium initiator, (b) an organoaluminum compound, (c) a barium compound, and (d) an organozinc compound.
U.S. Pat. No. 5,100,982 discloses a catalyst system which can be utilized in the polymerization of 1,3-butadiene monomer into trans-1,4-polybutadiene. This catalyst system is comprised of an organocobalt compound, an organoaluminum compound, a para-alkyl substituted phenol which contains from about 12 to about 26 carbon atoms, and carbon disulfide.
Lanthanide and actinide catalyst systems are considered to be xe2x80x9cpseudo-livingxe2x80x9d because polymers synthesized with such rare earth systems increase in molecular weight with increasing conversions. Conjugated diolefin monomers can be polymerized into rubbery polymers using such catalyst systems. More specifically, 1,3-butadiene can be polymerized into high cis-1,4-polybutadiene with a catalyst system which is comprised (i) an organoaluminum compound, (ii) an oganometallic compound which contains a lanthanide metal from Group III-B, such as neodymium, praseodymium, cerium, or gadolinium, and (iii) a labile halide ion. U.S. Pat. No. 4,663,405 discloses technique for controlling the molecular weight of polymers made with such lanthanide or actinide catalyst systems by conducting the polymerization in the presence of a vinyl halide.
U.S. Pat. No. 5,834,573 discloses a process for synthesizing trans-1,4-polybutadiene by polymerizing 1,3-butadiene monomer in the presence of a catalyst system which is comprised of cobalt (III) acetylacetonate, an organoaluminum compound, and a para-alkyl-substituted phenol, wherein the cobalt (III) acetylacetonate is mixed with a portion of the para-alkyl-substituted phenol prior to the polymerization and wherein the organoaluminum compound is mixed with the balance of the para-alkyl-substituted phenol prior to the polymerization.
U.S. Pat. No. 5,811,499 discloses a process for synthesizing cis-1,4-polybutadiene rubber which comprises polymerizing 1,3-butadiene in the presence of (a) an organocobalt compound, (b) a trialkylaluminum compound, and (c) hexafluoro-2-propanol.
High cis-1,4-polybutadiene rubber can be make with nickel catalyst systems which are comprised of (i) an organonickel compound, (ii) an organoaluminum compound, and (iii) a fluorine containing compound. U.S. Pat. No. 5,698,643 discloses such a nickel catalyst system where the molecular weight of the high cis-1,4-polybutadiene rubber produced is controlled by the addition of 1-butene, isobutylene, cis-2-butene, trans-2-butene, or allene.
U.S. Pat. No. 4,048,418 discloses a method of polymerizing conjugated diolefin monomers containing from 4 to about 12 carbon atoms into high molecular weight polymers by bringing the conjugated diolefin monomers into contact with a catalyst system consisting of (i) an iron-containing compound, (ii) an organometallic reducing agent from Group I or III of the Periodic Table, and (iii) a nitrogen-containing ligand.
U.S. Pat. No. 5,866,663 to Brookhart discloses a process for polymerizing olefins, such as ethylene, acyclic olefins, and/or selected cyclic olefins. The polymerizations of U.S. Pat. No. 5,866,663 are catalyzed by selected transition metal compounds, such as iron (II) compounds, and sometimes other co-catalysts.
This invention is based upon the unexpected discovery that certain catalyst systems which are comprised of (A) a transition metal compound selected from the group consisting of iron (II) compounds, iron (III) compounds, cobalt (II) compounds, cobalt (III) compounds, and nickel (II) compounds; (B) a ligand selected from the group consisting of certain azopyridines and certain iminopyridines; and (C) methylalumoxane can be used to catalyze the polymerization of diene monomers, such as 1,3-butadiene and isoprene, into polymers, such as high cis-1,4-polybutadiene rubber. Some representative examples of azopyridines that can be utilized in the catalyst systems of this invention include 2-phenylazopyridine, 4-methyl-2-phenylazopyridine, and 2,6-diphenylazopyridine.
This invention more specifically discloses a catalyst system which is comprised of (A) a transition metal compound selected from the group consisting of iron (II) compounds, iron (III) compounds, cobalt (II) compounds, cobalt (III) compounds, and nickel (II) compounds; (B) a ligand selected from the group consisting of (i) azopyridines of the structural formula: 
(ii) azopyridines of the structural formula: 
(iii) iminopyridines of the structural formula: 
and (iv) iminopyridines of the structural formula: 
wherein R represents a hydrogen atoms, a hydrocarbyl groups, or a substituted hydrocarbyl groups, and wherein R1 represents a hydrogen atom or a methyl group; and (C) methylalumoxane.
This invention also reveals a process for synthesizing a rubbery polymer which comprises polymerizing at least one diene monomer in the presence of a catalyst system which is comprised of (A) a transition metal compound selected from the group consisting of iron (II) compounds, iron (III) compounds, cobalt (II) compounds, cobalt (III) compounds, and nickel (II) compounds; (B) a ligand selected from the group consisting of (i) azopyridines of the structural formula: 
(ii) azopyridines of the structural formula: 
(iii) iminopyridines of the structural formula: 
and (iv) iminopyridines of the structural formula: 
wherein R represents a hydrogen atom, a hydrocarbyl group, or a substituted hydrocarbyl group, and wherein R1 represents a hydrogen atoms or a methyl groups; and (C) methylalumoxane.
The subject invention further discloses a process for synthesizing a polybutadiene rubber which comprises polymerizing 1,3-butadiene at a temperature which is within the range of about 10xc2x0 C. to about 100xc2x0 C. in the presence of a catalyst system which is comprised of (A) a transition metal compound selected from the group consisting of iron (II) compounds, iron (III) compounds, cobalt (II) compounds, cobalt (III) compounds, and nickel (II) compounds; (B) a ligand selected from the group consisting of (i) azopyridines of the structural formula: 
(ii) azopyridines of the structural formula: 
(iii) iminopyridines of the structural formula: 
and (iv) iminopyridines of the structural formula: 
wherein R represents a hydrogen atom, a hydrocarbyl group, or a substituted hydrocarbyl group, and wherein R1 represents a hydrogen atoms or a methyl groups; and (C) methylalumoxane.
The present invention further reveals a catalyst system which is comprised of (A) a transition metal compound selected from the group consisting of iron (II) compounds, iron (III) compounds, cobalt (II) compounds, cobalt (III) compounds, and nickel (II) compounds; (B) a ligand selected from the group consisting of (i) azopyridines of the structural formula: 
(ii) azopyridines of the structural formula: 
(iii) iminopyridines of the structural formula: 
and (iv) iminopyridines of the structural formula: 
wherein R represents a hydrogen atom, a hydrocarbyl group, a substituted hydrocarbyl group, or a heteroatom containing hydrocarbyl group wherein the heteroatom is selected from the group consisting of boron, nitrogen, sulfur, phosphorus, oxygen, and silicon, and wherein R1 represents a hydrogen atoms or a methyl groups; and (C) methylalumoxane.
Virtually any iron (II) compound, iron (III) compound, cobalt (II) compound, cobalt (III) compound, or nickel (II) compound can be used as the transition metal component in the catalyst systems of this invention. For instance, the transition metal compound can be an iron (II) or an iron (III) compound selected from the group consisting of monoacetyl ferrocene, di(4-aminobutyl)-cyclopentadienyl iron, aminoferrocene, (benzoylcyclopentadienyl)cyclopentadienyl iron, phenylferrocenylmethane, cyclopentadienyl iron, ferrocene monocarboxylic acid, (carboxylamidecyclopentadienyl)cyclopentadienyl iron, di(3-carboxypropionyl)cyclopentadienyl iron, chloromercuriferrocene, (p-chlorophenylcyclopentadienyl) cyclopentadienyl iron, cyanocyclopentadienyl)cyclopentadienyl iron, di[(3-cyanopropionyl)cyclopentadienyl]iron, cycloheptatrienyliron dicarbonyl, (cyclopentenylcyclopentadienyl)cyclopentadienyl iron, (cyclopentylcyclopentadienyl)cyclopentadienyl iron, 1,1xe2x80x2-di(acetylcyclopentadienyl) iron, 1,1xe2x80x2-dibenzhydrylferrocene, 1,1xe2x80x2-dibenzoylferrocene, 1,1xe2x80x2-dibenzylferrocene, ferrocene dicarboxylic acid, ferrocene 1,3-dicarboxylic acid, 1,1xe2x80x2-di(chloromercuri)ferrocene, 1,1xe2x80x2-di(p-chlorophenylcyclopentadienyl)iron, ferrocenyl-bis-phenyl methanol, 1,1xe2x80x2-di(methylcarboxycyclo-pentadienyl)iron, (1,3-diphenylcyclo-pentadienyl)cyclopentadienyl iron, 1,1xe2x80x2-diphenyl-dicyclopentadienyl iron, 1,1xe2x80x2-di(trimethylsilyl)ferrocene, ferrocene, ferrocenyl-acetic acid, 1,1xe2x80x2-ferrocenyl-diacetic acid, xcex1-ferrocenyl-ethyl alcohol, xcex1-ferrocenyl-propionic acid, formylcyclopentadienyl)cyclopentadienyl iron, phenyl-ferrocenyl methanol, hydroxymethylferrocene, p-hydroxyphenylcyclo-pentadienyl)cyclopentadienyl iron, (methylcarboxycyclopentadienyl)cyclopentadienyl iron, bis(methyl-isonitrile)tricarbonyl iron, (p-nitrophenylcyclopentadienyl)cyclopentadienyl iron, phenyl ferrocene, 1,3,1xe2x80x2,3xe2x80x2-tetraphenylferrocene, thiopheniron dicarbonyl, trimethylsilyl ferrocene, ferric, oxalate, ferric hexanoate, ferric octanoate, ferric decanoate, ferric stearate, ferric naphthenate, ferrous acetylacetonate, ferric acetylacetonate, ferric-1-ethoxy-1,3-butanedionate, ferrous dimethyl glyoxime, ferric chloride, ferrous chloride, ferric bromide, ferric fluoride, ferric phosphate, ferrous sulfate, iron tetracarbonyl, iron pentacarbonyl, and iron nonacarbonyl.
The ligands used in the catalyst systems of this invention can be azopyridines or iminopyridines. The azopyridines that can be used can be of the structural formula: 
or can be of the structural formula: 
wherein R represents a hydrogen atom, a hydrocarbyl group, a substituted hydrocarbyl group, or a heteroatom containing hydrocarbyl group wherein the heteroatom is selected from the group consisting of boron, nitrogen, sulfur, phosphorus, oxygen, and silicon, and wherein R1 represents hydrogen atoms or methyl groups. It is to be understood that each of the R groups in the ligand can be the same or different from other R groups in ligand and that each of the R1 groups in the ligand can be the same or different from other R1 groups in ligand. As used herein a xe2x80x9chydrocarbyl groupxe2x80x9d is a univalent group containing only carbon and hydrogen and a xe2x80x9csubstituted hydrocarbyl groupxe2x80x9d is a hydrocarbyl group that contains one or more substituent groups which are inert under the process conditions to which the compound containing these groups is subjected. In other words, the substituent groups do not substantially interfere with the polymerization reaction. In cases where R represents a hydrocarbyl group it will typically contain from 1 to about 30 carbon atoms and will more typically contain from 1 to about 20 carbon atoms. In cases where R represents a hydrocarbyl group it will preferably contain from 1 to about 6 carbon atoms and will more typically contain from 1 to about 4 carbon atoms. For instance, the hydrocarbyl group (R) can be a methyl group, an ethyl group, an iso-propyl group, a normal-propyl group, a normal-butyl group, an iso-butyl group, a tertiary-butyl group, a normal-pentyl group, a normal-hexyl group, or a phenyl group. It is generally preferred for R to represent a hydrogen atom or a methyl group (xe2x80x94CH3).
The iminopyridines that can be used as the ligands in the catalyst systems of this invention can be of the structural formula: 
or can be of the structural formula: 
wherein R represents a hydrogen atom, a hydrocarbyl group, or a substituted hydrocarbyl group, and wherein R1 represents hydrogen atoms or methyl groups. It is to be understood that each of the R groups in the ligand can be the same or different from other R groups in ligand and that each of the R1 groups in the ligand can be the same or different from other R1 groups in ligand. As used herein a xe2x80x9chydrocarbyl groupxe2x80x9d is a univalent group containing only carbon and hydrogen and a xe2x80x9csubstituted hydrocarbyl groupxe2x80x9d is a hydrocarbyl group that contains one or more substituent groups which are inert under the process conditions to which the compound containing these groups is subjected. In other words, the substituent groups do not substantially interfere with the polymerization reaction. In cases where R represents a hydrocarbyl group it will typically contain from 1 to about 30 carbon atoms and will more typically contain from 1 to about 20 carbon atoms. In cases where R represents a hydrocarbyl group it will preferably contain from 1 to about 6 carbon atoms and will more typically contain from 1 to about 4 carbon atoms. For instance, the hydrocarbyl group (R) can be a methyl group, an ethyl group, an iso-propyl group, a normal-propyl group, a normal-butyl group, an iso-butyl group, a tertiary-butyl group, a normal-pentyl group, a normal-hexyl group, or a phenyl group. It is generally preferred for R to represent a hydrogen atom or a methyl group (xe2x80x94CH3). Some highly preferred azopyridine compounds that can be utilized as the ligand in the catalyst systems of this invention include 2-phenylazopyridine, 4-methyl-2-phenylazopyridine, and 2,6-diphenylazopyridine.
The methylalumoxane (MAO) used in the catalyst systems of this invention can be of the general structural formula (CH3)2xe2x80x94AlOxe2x80x94[Al(CH3)O]nxe2x80x94Al(CH3)2, wherein n represents an integer from 5 to 20. The methylalumoxane used will typically have a formula selected from the group consisting of 
wherein Rxe2x80x3 represents an alkyl group containing from 1 to about 10 carbon atoms, and wherein n represents an integer from 1 to about 40 and preferably 3 to about 20. In co-catalysts of the MAO type which are of the formula: 
R* will preferably contain from 1 to about 4 carbon atoms with methyl groups being most preferred.
The molar ratio of the aluminum in the methylalumoxane to the iron or cobalt will typically be within the range of about 10:1 to about 10,000:1. The molar ratio of the aluminum in the methylalumoxane to the iron or cobalt will more typically be within the range of about 100:1 to about 5,000:1. The molar ratio of the aluminum in the methylalumoxane to the iron or cobalt will preferably be within the range of about 400:1 to about 2,000:1. In commercial applications, the molar ratio of the aluminum in the methylalumoxane to the iron or cobalt will normally be within the range of about 50:1 to about 500:1.
In using the catalyst systems of this invention to polymerize monomers into polymers, the molar ratio of the iron or cobalt in the catalyst to the monomer will typically be within the range of about 0.001 mmol per 100 grams of monomer to about 10 mmol per 100 grams of monomer. The molar ratio of iron or cobalt in the catalyst to the monomer will more typically be within the range of about 0.01 mmol per 100 grams of monomer to about 10 mmol per 100 grams of monomer. The molar ratio of iron or cobalt in the catalyst to the monomer will preferably be within the range of about 0.05 mmol per 100 grams of monomer to about 1 mmol per 100 grams of monomer. The molar ratio of iron or cobalt in the catalyst to the monomer will more preferably be within the range of about 0.1 mmol per 100 grams of monomer to about 0.5 mmol per 100 grams of monomer.
The catalyst systems of this invention can be used to polymerize virtually any type of diene monomer, such as conjugated diolefin monomers. The conjugated diolefin monomers that can be polymerized into polymers with the catalyst systems of this invention are of the general structural formula: 
wherein R is selected from the group consisting of hydrogen atoms, alkyl groups (including cycloalkyl groups) alkaryl groups, or aryl groups containing from 1 to about 8 carbon atoms, and wherein Y and Yxe2x80x2 can be the same of different and represent hydrogen toms or alkyl groups containing from 1 to about 4 carbon atoms. Some representative examples of conjugated diolefin monomers that can be polymerized with the catalyst systems of this invention include 1,3-butadiene, isoprene, piperylene, 2-methyl-1,3-pentadiene, 2-ethyl-1,3-butadiene, 4-butyl-1,3-pentadiene, 2,3-dimethyl-1,3-pentadiene, 1,3-hexadiene, 1,3-octadiene, 1-phenyl-1,3-butadiene, and the like. The catalyst systems of this invention can also be used to copolymerize vinyl aromatic monomers with diene monomers. For instance, the catalyst systems of this invention can be used to copolymerize 1,3-butadiene and styrene to make styrene-butadiene rubber.
The polymerizations of this invention can be carried out over a broad temperature range of from about 0xc2x0 C. to about 100xc2x0 C. The polymerization will typically be carried out at a temperature which is within the range of about 30xc2x0 C. to about 90xc2x0 C. It is normally preferred to conduct the polymerization at a temperature which is within the range of about 50xc2x0 C. to about 80xc2x0 C.
The polymerizations of this invention will normally be carried out in a hydrocarbon solvent that can be one or more aromatic, paraffinic or cycloparaffinic compounds. These solvents will normally contain from 4 to 10 carbon atoms per molecule and will be liquid under the conditions of the polymerization. Some representative examples of suitable organic solvents include pentane, isooctane, cyclohexane, methylcyclohexane, isohexane, n-heptane, n-octane, n-hexane, benzene, toluene, xylene, ethylbenzene, diethylbenzene, isobutylbenzene, petroleum ether, kerosene, petroleum spirits, petroleum naphtha, and the like, alone or in admixture. The polymerizations of this invention can also be conducted as bulk phase or gas phase reactions with the catalyst system being either supported or unsupported.
In such solution polymerization, there will normally be from 10 to 40 weight percent monomers in the polymerization medium. Such polymerization media are, of course, comprised of the organic solvent and monomers. In most cases, it will be preferred for the polymerization medium to contain from 15 to 25 weight percent monomers. It is generally more preferred for the polymerization medium to contain 30 to 35 weight percent monomers.
The polymerization is conducted for a length of time sufficient to permit substantially complete polymerization of monomers. In other words, the polymerization is normally carried out until high conversions are attained. The polymerization can then be terminated using a standard technique. For instance, the polymerization can be terminated with a conventional noncoupling type of terminator, such as water, an acid, a lower alcohol, and the like.
After the copolymerization has been completed, the polymer can be recovered from the organic solvent. The polymer can be recovered from the organic solvent and residue by means such as decantation, filtration, centrification and the like. It is often desirable to precipitate the polymer from the organic solvent by the addition of lower alcohols containing from about 1 to about 4 carbon atoms to the polymer solution. Suitable lower alcohols for precipitation of the polymer from the polymer cement include methanol, ethanol, isopropyl alcohol, normal-propyl alcohol and t-butyl alcohol. After the polymer is recovered from the solution, steam-stripping can be employed to reduce the level of volatile organic compounds in the polymer.